1. Field of the Invention
This invention relates to a continuously variable transmission which is employed as a transmission of an automobile or the like.
2. Description of the Related Art
A troidal-type continuously variable transmission employed as a vehicle transmission or the like has been disclosed, for instance, by Japanese Patent Publications Nos. Hei. 6-506042 and Hei. 1-169169. Each of those continuously variable transmissions has an input shaft which is rotated by a drive source, an output shaft which outputs a driving force attributing to the rotation of the input shaft; a speed ratio changing device, namely, a variator which is arranged between the input shaft and the output shaft, and a planet gear mechanism.
What is disclosed in Japanese Patent Publication No. Hei. 6-506042 is a gear neutral system which performs driving force circulation in a low speed mode. Its planet gear mechanism has a low speed clutch and a high speed clutch. When the low speed clutch is connected, and the high speed clutch is disconnected (released), the driving force is transmitted from the planet gear mechanism to the output shaft, and a part of the driving force is transmitted to the variator.
On the other hand, what is disclosed by Japanese Patent Publication No. Hei. 1-169169 is a power split system which perform driving force circulation in a high speed mode. Its planet gear system has a low speed clutch, and a high speed clutch. When the low speed clutch is disconnected while the high speed clutch is connected, the rotational driving force of the input shaft is transmitted to the output shaft directly through the planet gear mechanism (instead of the variator), and a part of the driving force is transmitted to the variator.
That is, in any one of the systems, the low speed clutch and the high speed clutch are provided, and in the case of the mode change, when the rotations in the clutch section are equal to each other, the clutch connection is changed.
However, the conventional troidal-type continuously variable transmission has no means which confirms whether or not a first power transmitting system which is inputted to the planet gear mechanism through the variator is equal in the number of revolutions to a second power transmitting system which is inputted directly (not through the variator) to the planet gear mechanism. In addition, even when a predetermined change gear ratio is not reached, or the gear change is over, or the gear change becomes impossible because the variator becomes out of order, the clutch is changed. Therefore, the clutch is not connected, or damaged. Furthermore, if the clutch is changed when the numbers of revolutions are different, then a gear change shock occurs, which makes the driver or other persons on the vehicle feel bad.